Apparatus for the purification of water contaminated with oil

ABSTRACT

An installation for cleaning oil-polluted water, in particular at oil and gas production plants, is provided with a distillation column having a polluted water feed and at least one contact packing above which the outlet of the polluted water feed is located, a vapor discharge, a clean water outlet and a measuring device for the analysis of the water from the clean water outlet.

This application is the national phase of international application Ser.No. PCT/NL95/00404, which has an international filing date of Nov. 27,1995 and claiming priority to Dutch application Ser. No. NL 9401977filed on Nov. 25, 1994.

The invention relates to an installation for cleaning oil-pollutedwater, in particular near oil and gas production plants.

FR-A-2.267.285 concerning a process for the treatment of polluted water,is a multistage process operating in a first step at underpressure andin a final step under vacuum to obtain a concentrated residue for use inlandfill. The process according to this citation employs various flows,i.e. a flow with hydrocarbons having a boiling temperature less than 95°C., a flow having hydrocarbons with boiling temperature between 95 and110° C., and a flow having hydrocarbons with a boiling temperature inexcess of 110° C.

U.S. Pat. No. 4,019,977 concerns an oil reclamation process in which theoil containing liquid contaminants, principally water, is evaporatedentirely to separate the oil from the liquid.

Nowadays off shore and on shore production platforms utilizeinstallations such as skimmers, floatation units, hydrocyclones,centrifuges, etc. to separate dispersed oil from production waterreleased during the production of oil and gas. These installations areusually not capable of continuously decreasing the oil concentration inwater to about 40 ppm. This 40 ppm limit is the maximum value allowed bymany authorities.

It is the object of the invention to provide an installation of the kindmentioned in the preamble whereby not only a high standard of cleaningcan be achieved, but whereby this cleaning is achieved in a veryenergy-efficient way, and whereby also automatic control is possible.

To this end the installation according to the invention is characterizedby a distillation column having internal or external heating means aswell as means for the generation of a controlled underpressure in thedistillation column, and comprising a polluted water feed and at leastone contact packing above which the polluted water feed exits, a vapourdischarge and a clean water outlet; and a measuring device for theanalysis of the water from the clean water outlet.

By means of the distillation column energy-efficient separation of alarge percentage of aromatic and aliphatic compounds from the water isattained, thus meeting high cleaning requirements. Nowadays continuouson-line equipment is available for measuring. In this manner the oilcontent in water can be measured continuously instead of 16 times amonth, as is now required by many authorities. By means of certain kindsof analysis devices the content of aliphatic and aromatic compounds inthe cleaned water can be measured separately or combined. In addition,the output signals of both devices can be transmitted continuously to acentral platform. The performance of the cleaning installation cantherefore be monitored and controlled from a distance. Helicopterflights to the various unmanned production platforms for taking samplesfor laboratory analysis, as occurs with the known off-shoreinstallations, are therefore no longer necessary. Weekly or monthlycalibration of the measuring device according to the invention suffices.

The internal heating means applied may, for instance, be electricheating. However, sometimes the application of external heating meansmay be more desirable; viz. if gas is released on the platform, it maybe utilized for heating by means of a separate reboiler.

The installation according to the invention is capable of effectivelyseparating oil from water, whereby the heating means and the pressuredecreasing means together realize at least partial evaporation of thepolluted water, leading to optimal separation. Further, theunderpressure lowers the boiling point of the volatile hydrocarboncomponents so that for instance, in the distillation column, instead ofheating to the boiling point of water, a much lower temperature in therange of 40-60° C. and in some applications even lower, suffices. Forsome organic components the separation factor is substantially improvedif separation is carried out at decreased pressure and temperature.Because many organic compounds have boiling points below that of water,most organic compounds will be concentrated in the vapour phase.However, as many organic compounds together with water form azeotropiccompounds, heavy organic compounds with boiling points higher than waterwill also leave the column in the vapour phase. In this way most of theorganic compounds in the polluted water feed will be removed without allthe water having to evaporate. The object of the invention is even toevaporate less than 20% of the incoming water. Under certain conditionseven only 5% evaporation is possible. Due to the packing there is alarge contact surface between the fluid and the vapour phase. Thisensures that the water flowing downward, in counterflow to the risingvapour, will be cleaned substantially in a very efficient manner so thatthe clean water outlet may be connected directly to the bottom of thedistillation column. After-cleaning is generally unnecessary;nonetheless, an after-cleaner in the form of a UV-oxidation unit, may beincorporated in the clean water outlet, which will then be placed beforethe measuring device. Furthermore, according to the invention apre-cleaning installation may be incorporated in the polluted water feedin order to supply the distillation column with water from which dustparticles and part of the oil have been removed so that the distillationcolumn is a little less heavily burdened.

The invention will hereafter be elucidated by means of the drawingsillustrating three embodiments of the installation according to theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are process diagrams of three embodiments of aninstallation for cleaning oil-polluted water according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the different embodiments comparable parts are indicated by the samereference number.

FIG. 1 shows a first embodiment of the installation according to theinvention. At 1 the polluted water arrives from a collecting tank (notshown) and is collected in a polluted water tank 2. With the aid of apump 4 provided in the pipe 3 the polluted water is conducted into apre-separation unit 5 where either mechanically or hydraulically solidparticles and possibly oil are separated from the water. Thispre-separation unit may take the form of a filter, a hydrocyclone, acentrifuge or a sieve separator or the like. Such a pre-separation unitcan already considerably reduce the amount of pollution. With the aid ofthe pump 6 the separated oil phase is conducted via the pipe 7 to a tank8 for dirty oil. With the aid of the pump 9 the cleaned water is drainedaway from the pre-separation unit 5 via the pipe 10, and the oil contentin the water of the pipe 10 is measured by means of an analysisinstallation 11. If the oil content in the water exceeds a predeterminedlevel, then the production water is, via a pipe 13, conducted back tothe polluted water tank 2 by means of a threeway valve 12, controlled bythe analysis installation 11. If the oil content in the water remainsbelow the predetermined limit, then the water is pumped further via thethreeway valve 12 through the pipe 10 to an intermediate storage tank14.

A pipe 15 provided with a pump 16 for pumping on the pre-treatedproduction water is connected to the intermediate storage tank 14. Thepipe 15 finally connects to a pipe 17, at the feed side 18 from whichsea water can be supplied which by means of a pump 19 can be pumped tothe outlet side of the pipe 17. The outlet side of this pipe 17, throughwhich optionally fresh sea water (in the case of an off shoreinstallation) for the purpose of starting up the whole installation orpre-treated production water from the pipe 15 can be drained away, endsin the distillation column 20, which is the heart of the installation.The outlet side of the pipe 17 is provided with a sprinkler head 21distributing the water supplied to the distillation column 20, whichwater is preferably sprinkled onto a fluid distributor 22, such as agrid or a perforated plate, in order to promote a uniform distributionof moisture. Under the fluid distributor 22 a packing 23 of knownconstruction is provided, which packing serves to provide a very largecontact area in a small space. The fluid distributor ensures that thepacking 23 is moistened even better.

The prevailing pressure in the distillation column 20 is preferably anunderpressure in order to achieve evaporation of the componentscontained in the supplied production water without necessitating aconsiderable rise in temperature by means, in this case, of an electricheating installation 24 near the bottom of the distillation column 20.Most organic compounds will be concentrated in the vapour phase becausethe boiling point of many organic compounds is lower than that of water.However, many organic compounds together with water form azeotropiccompounds, so that heavy organic compounds having boiling points higherthan water, will also leave the distillation column 20 in the vapourphase. In this way most organic compounds present in the suppliedproduction water will be removed without evaporating too much water. Theaim is that of the water itself less than 20%, and preferably only 5% isevaporated. This lowers the energy consumption considerably. The waterthat is not evaporated and from which most of the organic compounds areremoved, will collect on the bottom of the distillation column 20. Theelectric heating installation is located below the surface of thiscollected water and the level controls 25 ensure that the water level onthe bottom of the distillation column 20 stays within certain limits bycontrolling a pump 26 in an outlet pipe 27 or a valve 54 therein.

The outlet pipe 27 further comprises a heat exchanger 28 through which,in a separate pipe system, the pre-cleaned water of pipe 15 flows, inorder to pre-heat the pre-cleaned water 15 with the aid of the waterwhich was warmed up in the distillation column 20. From the outlet pipe27 the cleaned water flows into the tank 29. A pipe 31 provided with apump 30 is connected to the tank 29, for pumping the cleaned water to anoptional, and usually superfluous, after-cleaning installation,comprised in this case of a UV-oxidation unit 32. This UV-oxidation uniteliminates any remaining aromatic compounds in the water. Before thewater coming from this oxidation unit 32 is discharged again, thecontent of aliphatic and aromatic compounds is measured in the analysisinstallation 33 for aliphatics and in the analysis installation 34 foraromatics. These analysis installations 33 and 34 constantly monitor thealiphatics and aromatics contents enabling them, with the aid of thethreeway valve controlled by them, to determine whether the sufficientlycleaned water is discharged at 37 via the pipe 36 into, for instance thesea or whether, if insufficiently cleaned, it is returned via a pipe 38to an intermediary tank 14 for pre-cleaned water in order to beretreated in the distillation column 20. The entire installation can bemonitored and controlled from a distance because the output signals fromthe analysis installations 33 and 34 can be sent to a central controlplatform.

Returning to the distillation column 20 the drawing further shows thatthe vapour rising upward, thus in counterflow with the water flowingdown, and therefore establishing a good contact, can be discharged inthe top of the distillation column 20 with the aid of a vapour dischargepipe 39 comprising a vacuum pump 40 to generate the underpressure in thedistillation column 20 and for drawing off the vapour through the vapourdischarge pipe 39. The vapour discharged from the vacuum pump 40 is inmost cases very hot and can be utilized in the heat exchanger 41 tofurther pre-heat the pre-cleaned production water flowing through pipe15 and the heat exchanger 41. The somewhat cooled vapour is subsequentlycondensed by means of cooling in a cooling installation 42, whereby thecondensate divides into two phases, viz. an organic phase and a waterphase. The two phases are then separated in a two-phase separator 43such as a settler or a hydrocyclone, a centrifuge, a decantationinstallation or the like. With the aid of a pump 44 the organic phase isthen drained away via a pipe 45 to a tank 8 for dirty oil. The pump 47pumps the water phase through the pipe 46 to the pipe 15 in order to bereturned to the distillation column 20.

Of course, as is usual with such installations, all kinds of safetyprovisions (not shown here) are provided. However, FIG. 1 does show thatall tanks (2,8,14 and 29) are provided with level controls 48 which,when the level in a particular tank is too high, will open acorresponding overflow pipe 49 in order to let the surplus fluid flowaway at 50 to the collector tank for the production water. The fluidcollected in the tank 8 as dirty oil, is during normal operation emptiedvia pipe 51 and at 52 the dirty oil is either led to a special tank inwhich the oil is collected for further treatment or drainage, or isreturned to the production process.

FIG. 2 shows a slightly adapted variant of the installation according toFIG. 1. In this variant the installation column 20 is provided with twopackings 23 and 23A, wherein the sprinkler element 21 for thepre-cleaned production water and the fresh seawater discharges above thelower packing 23, while a sprinkler element 53, attached to the end ofpipe 46, discharges above the upper packing 23A, returning the waterphase from the two-phase separator directly into the distillation column20, and preferably onto a fluid distributer 22A such as a grid or aperforated plate. In this way the returned water is led through a heatexchanger 41 and is thus reheated.

It will be obvious that, depending on the application, the distillationcolumn 20 may be provided with even more packings 23, 23A and fluiddistributers 22, 22A. It is also possible in certain applications, wherethe production water does not contain too many dust particles or oil, toomit the pre-separation installation and to conduct the production waterdirectly into the distillation column 20. Further additions or omissionsare also conceivable. This is illustrated in FIG. 3, showing analternative embodiment of the installation according to the invention,in which the number of installation parts applied is considerablyreduced. At reference number 1 polluted water arrives at theinstallation from a production platform and is received in pollutedwater tank 2. From this tank 2 the polluted water is conducted via pipe3 through a filter 5 for the removal of solid particles, whereby thetransport energy for the transport of the polluted water is provided bypump 16. In order to be warmed up the polluted water is led through aheat exchanger 28 and further via pipe 15 to a sprinkler element 21 inthe distillation column 20. The heat exchanger 28, on the other hand, isfed with heated clean water which is obtained from the distillationcolumn 20 via pipe 27 by means of a pump 26 and is led to the tank 29,from which by means of pump 30, the clean water is then led to theanalysis installations 33 and 34 for measuring the content of aliphaticand aromatic compounds. The polluted water which is brought into thedistillation column 20 by means of the sprinkler element 21, issprinkled onto a fluid distributer 22 under which is provided a packing23 where intensive interaction is obtained between the polluted waterand the vapour fraction generated in the distillation column 20. Thisvapour fraction is obtained with the aid of heating means 24 placedoutside of the distillation column 20 and comprises a reboiler fed withelectricity or gas, and which serves to heat clean water from thedistillation column 20, which water leaves the same at the bottom viapipe 27 and is returned, after passing the heating means 24, into thedistillation column 20 under the packing 23. The vapour fraction leavesthe distillation column 20 at the top via pipe 39 and is conductedthrough a condenser 42 where this vapour fraction condenses and splitsinto two phases, viz. an organic phase and a water phase. The two phasesare subsequently separated in a two-phase separator 43, for instance ina settler, to which a vacuum pump 40 is connected to provide both theunderpressure in the distillation column 20 and to implement thetransport of the vapour fraction. It is preferable to place the vacuumpump 40 after the two-phase separator 43 rather than in the pipe 39immediately after the distillation column 20, because then the pump 40may be much smaller, so that a substantial saving in expenditure may berealized. The oil fraction separated in the two-phase separator 43 istransported by means of a pump 44 to a tank 8. The watery fraction whichmay still contain oil particles, is returned by means of a pump 47 tothe polluted water tank 2 via a pipe 46 which is connected to thetwo-phase separator 43.

The foregoing shows that the invention provides an installation which,by means of relatively simple equipment achieves very good cleaning ofthe production water, so that the cleaned water can be dischargeddirectly. Of course, the installation according to the invention is notonly useful with gas and oil production at sea, but also with a similarproduction on land. The installation can also be adapted for use withdifferent ordinary installations on land for the separation of oil andwater. The invention is not limited to the embodiments shown in thedrawings and described in the embodiment examples, which may be variedin different ways without departing from the scope of the invention asspecified in the appended claims.

We claim:
 1. An installation for cleaning oil-polluted water, saidinstallation comprising:a distillation column comprising means forgenerating a controlled underpressure in said column, heating means, apolluted water feed, at least one contact packing above which an outletof said polluted water feed is located, a vapor discharge, and a cleanwater outlet; and a measuring device for analysis of water from theclean water outlet; and wherein said vapor discharge comprises a coolinginstallation, a two-phase separator, and a water return; and whereinsaid means for generating a controlled underpressure is downstream fromsaid two-phase separator.
 2. The installation according to claim 1,wherein said heating means comprises a reboiler connected, for feedingand receiving, with said column.
 3. The installation according to claim1, wherein said polluted water feed discharges via a sprinkler element.4. The installation according to claim 3, wherein said sprinkler elementis above a fluid distributor.
 5. The installation according to claim 4,wherein said sprinkler element is above a perforated plate.
 6. Theinstallation according to claim 3, wherein said water return dischargesinto said polluted water feed.
 7. The installation according to claim 3,wherein said water return discharges into said column via a furthersprinkler element.
 8. The installation according to claim 7, whereinsaid further sprinkler element is above said sprinkler element of saidpolluted water feed.
 9. The installation according to claim 8, whereinsaid further sprinkler element is above said sprinkler element of saidpolluted water feed and a packing located above it.
 10. The installationaccording to claim 3, wherein said water return discharges into apolluted water tank which, during operation, feeds said polluted waterfeed.
 11. The installation according to claim 1, additionally comprisinga heat exchanger between members of a combination selected from thegroup consisting of said vapor discharge and said polluted water feed,said clean water outlet and said polluted water feed, and said vapordischarge and said water return.
 12. The installation according to claim1, wherein said clean water outlet is connected at a bottom of saidcolumn.
 13. The installation according to claim 1, wherein said cleanwater outlet comprises a UV-oxidation unit as after-cleaner locatedin-stream before said measuring device.
 14. The installation accordingto claim 1, wherein said polluted water feed comprises a pre-separationinstallation.
 15. The installation according to claim 1, wherein saidmeasuring device comprises an analyzer for aliphatic compounds, ananalyzer for aromatic compounds, and means for sending signals to acontrol room situated at a distance from said installation.
 16. Theinstallation according to claim 1, wherein said vapor dischargedischarges from said column a maximum of 20% of water fed into saidcolumn via said polluted water feed.
 17. The installation according toclaim 16, wherein said vapor discharge discharges from said column amaximum of 5% of water fed into said column via said polluted waterfeed.
 18. An installation for cleaning oil-polluted water, saidinstallation comprising:a distillation column comprising means forgenerating a controlled underpressure in said column, heating means, apolluted water feed, at least one contact packing above which an outletof said polluted water feed is located, a vapor discharge, and a cleanwater outlet; and a measuring device for analysis of water from theclean water outlet; and wherein said clean water outlet comprises aUV-oxidation unit as after-cleaner located in-stream before saidmeasuring device.
 19. The installation according to claim 18, whereinsaid heating means comprises a reboiler connected, for feeding andreceiving, with said column.
 20. The installation according to claim 18,wherein said polluted water feed discharges via a sprinkler element. 21.The installation according to claim 20, wherein said sprinkler elementis above a fluid distributor.
 22. The installation according to claim21, wherein said sprinkler element is above a perforated plate.
 23. Theinstallation according to claim 20, wherein said water return dischargesinto said polluted water feed.
 24. The installation according to claim20, wherein said water return discharges into said column via a furthersprinkler element.
 25. The installation according to claim 24, whereinsaid further sprinkler element is above said sprinkler element of saidpolluted water feed.
 26. The installation according to claim 25, whereinsaid further sprinkler element is above said sprinkler element of saidpolluted water feed and a packing located above it.
 27. The installationaccording to claim 20, wherein said water return discharges into apolluted water tank which, during operation, feeds said polluted waterfeed.
 28. The installation according to claim 18, wherein said vapordischarge comprises a cooling installation, a two-phase separator, and awater return.
 29. The installation according to claim 28, wherein saidmeans for generating a controlled underpressure is downstream from saidtwo-phase separator.
 30. The installation according to claim 18,additionally comprising a heat exchanger between members of acombination selected from the group consisting of said vapor dischargeand said polluted water feed, said clean water outlet and said pollutedwater feed, and said vapor discharge and said water return.
 31. Theinstallation according to claim 18, wherein said clean water outlet isconnected at a bottom of said column.
 32. The installation according toclaim 18, wherein said polluted water feed comprises a pre-separationinstallation.
 33. The installation according to claim 18, wherein saidmeasuring device comprises an analyzer for aliphatic compounds, ananalyzer for aromatic compounds, and means for sending signals to acontrol room situated at a distance from said installation.
 34. Theinstallation according to claim 18, wherein said vapor dischargedischarges from said column a maximum of 20% of water fed into saidcolumn via said polluted water feed.
 35. The installation according toclaim 34, wherein said vapor discharge discharges from said column amaximum of 5% of water fed into said column via said polluted waterfeed.
 36. An installation for cleaning oil-polluted water, saidinstallation comprising:a distillation column comprising means forgenerating a controlled underpressure in said column, heating means, apolluted water feed, at least one contact packing above which an outletof said polluted water feed is located, a vapor discharge, and a cleanwater outlet; and a measuring device for analysis of water from theclean water outlet; and wherein said measuring device comprises ananalyzer for aliphatic compounds, an analyzer for aromatic compounds,and means for sending signals to a control room situated at a distancefrom said installation.
 37. The installation according to claim 36,wherein said heating means comprises a reboiler connected, for feedingand receiving, with said column.
 38. The installation according to claim36, wherein said polluted water feed discharges via a sprinkler element.39. The installation according to claim 38, wherein said sprinklerelement is above a fluid distributor.
 40. The installation according toclaim 39, wherein said sprinkler element is above a perforated plate.41. The installation according to claim 38, wherein said water returndischarges into said polluted water feed.
 42. The installation accordingto claim 38, wherein said water return discharges into said column via afurther sprinkler element.
 43. The installation according to claim 42,wherein said further sprinkler element is above said sprinkler elementof said polluted water feed.
 44. The installation according to claim 43,wherein said further sprinkler element is above said sprinkler elementof said polluted water feed and a packing located above it.
 45. Theinstallation according to claim 38, wherein said water return dischargesinto a polluted water tank which, during operation, feeds said pollutedwater feed.
 46. The installation according to claim 36, wherein saidvapor discharge comprises a cooling installation, a two-phase separator,and a water return.
 47. The installation according to claim 46, whereinsaid means for generating a controlled underpressure is downstream fromsaid two-phase separator.
 48. The installation according to claim 36,additionally comprising a heat exchanger between members of acombination selected from the group consisting of said vapor dischargeand said polluted water feed, said clean water outlet and said pollutedwater feed, and said vapor discharge and said water return.
 49. Theinstallation according to claim 36, wherein said clean water outlet isconnected at a bottom of said column.
 50. The installation according toclaim 36, wherein said clean water outlet comprises a UV-oxidation unitas after-cleaner located in-stream before said measuring device.
 51. Theinstallation according to claim 36, wherein said polluted water feedcomprises a pre-separation installation.
 52. The installation accordingto claim 36, wherein said vapor discharge discharges from said column amaximum of 20% of water fed into said column via said polluted waterfeed.
 53. The installation according to claim 52, wherein said vapordischarge discharges from said column a maximum of 5% of water fed intosaid column via said polluted water feed.
 54. An installation forcleaning oil-polluted water, said installation comprising:a distillationcolumn comprising means for generating a controlled underpressure insaid column, heating means, a polluted water feed, at least one contactpacking above which an outlet of said polluted water feed is located, avapor discharge, and a clean water outlet; and a measuring device foranalysis of water from the clean water outlet; and wherein saidsprinkler element is above a fluid distributor; and wherein said waterreturn discharges into said column via a further sprinkler elementlocated above said sprinkler element of said polluted water feed and apacking located above it.
 55. The installation according to claim 54,wherein said heating means comprises a reboiler connected, for feedingand receiving, with said column.
 56. The installation according to claim54, wherein said polluted water feed discharges via a sprinkler element.57. The installation according to claim 56, wherein said sprinklerelement is above a perforated plate.
 58. The installation according toclaim 54, wherein said water return discharges into said polluted waterfeed.
 59. The installation according to claim 54, wherein said waterreturn discharges into a polluted water tank which, during operation,feeds said polluted water feed.
 60. The installation according to claim54, wherein said vapor discharge comprises a cooling installation, atwo-phase separator, and a water return.
 61. The installation accordingto claim 60, wherein said means for generating a controlledunderpressure is downstream from said two-phase separator.
 62. Theinstallation according to claim 54, additionally comprising a heatexchanger between members of a combination selected from the groupconsisting of said vapor discharge and said polluted water feed, saidclean water outlet and said polluted water feed, and said vapordischarge and said water return.
 63. The installation according to claim54, wherein said clean water outlet is connected at a bottom of saidcolumn.
 64. The installation according to claim 54, wherein said cleanwater outlet comprises a UV-oxidation unit as after-cleaner locatedin-stream before said measuring device.
 65. The installation accordingto claim 54, wherein said polluted water feed comprises a pre-separationinstallation.
 66. The installation according to claim 54, wherein saidmeasuring device comprises an analyzer for aliphatic compounds, ananalyzer for aromatic compounds, and means for sending signals to acontrol room situated at a distance from said installation.
 67. Theinstallation according to claim 54, wherein said vapor dischargedischarges from said column a maximum of 20% of water fed into saidcolumn via said polluted water feed.
 68. The installation according toclaim 67, wherein said vapor discharge discharges from said column amaximum of 5% of water fed into said column via said polluted waterfeed.